A study design in which a population at risk is examined to identify diseased as well as non-diseased individuals. These sub-groups are categorized as exposed or not exposed to the suspected factor and then followed for a period to identify who develops the disease and who does not within that period.

The purpose is to determine the association between a risk factor and the disease. This type of cohort study may be described as both longitudinal and prospective. Some special cases of cohort studies are retrospective rather than concurrent.